The concept of sucking frail material such as fish in a slurry through an inlet into a chamber and then forcing the fish from the chamber by applying air pressure to the chamber to drive the contents of the chamber out the outlet with the inlet valve closed is described for example in U.S. Pat. No. 3,871,332 issued Mar. 18, 1975 Hayashi.
In the system described in the Hayashi patent relatively elaborate controls are required and the operation is triggered by means of a float suspended within the chamber and responding to the level of liquid to activate a control mechanism when the level sensed by the float reaches a preset upper and a preset lower limit. The control mechanism opens and closes the various valves to apply either negative or positive air pressure to the chamber and open and close the inlet and outlet valves depending on the operating mode in which the pump is being operated.
The inlet and outlet valves used in this system are check valves which open and close depending on the pressure in the chamber. This arrangement was found to be unsatisfactory in practice as fish did not always clear the check valves and if the valve attempted to close with a fish caught therein the fish would either prevent closing of the valve rendering the pump inoperative or would be cut or damaged in some way to permit closing thereby reducing the value of the fish.
To overcome this problem of fish tampering with the operation of the check valves and damage being inflicted on the fish by the valves in closing an elaborate system of pumping water per se through each check valve before it was closed was installed. This water flushed the valves clean before they were closed and made the system operative but clumsy while requiring elaborate controls and reducing the reliability and capacity of the pump by reducing its availability for pumping.
U.S. Pat. No. 4,517,099 issued May 14, 1985 to Breckner provides a significant improvement by providing a specific location for a check valve in the inlet thereby because of the slope of the passages leading to and away from the check valve, the check valve automatically clears itself by gravity when the system is operated. This system is very effective but requires an installation wherein the attitude of the pump structure particularly the check valve is preset at least within certain limits since gravity functions to clear the valve. This also necessitated that the inlet to the chamber be located adjacent the upper end of the chamber so that the in feed conduit had to pass to the upper end of the chamber. Thus while this system is effective for many operations and requires a reasonably simple control system it is not completely suitable for a pump that is to be suspended for example from a boom via cables as is required for certain operations, nor is it as compact as one might desire for installation for example in the hold of a ship.
Bladder valves or as they are sometimes called, pinch valves have been in use for many years in various industries but never in connection with pumping frail material. Examples of such bladder valves are shown in U.S. Pat. No. 4,268,005 issued May 19, 1981 to Raftis et al or U.S. Pat. No. 4,135,550 issued Jan. 23, 1975 to Anderson.
U.S. Pat. No. 3,007,416 issued Nov. 7, 1961 to Childs discloses a type of pump that uses two bladder type valves positioned one on the inlet and the other on the outlet side of a flexible tubular element that is deformed to increase and decrease the size of the interior of the element so that the element functions to suck and reject fluid.
The term frail material as used in the present disclosure is intended to describe material that may be damaged by valves or its value reduced when caught in a valve and interfere with the valve as it is closing, in particular food products such as fish, vegetables, fruit and the like.